Sighting device for aircraft



Mar. 27, 1923 1,449,527

0. MACKENSEN SIGHTING DEVICE FOR AIRCRAFT Filed Aug; 15, 1921'. 2 sheets-sheet 1 Mar. 27, 1923 1,449,527

0. MACKENSEN SIGHTING DEVICE FOR AIRCRAFT Filed Aug. 13,1921. 2 sheets-sheet 2 m which has a Patented Mar. 27, 1923.-

onrran STATES 1,449,527 PATENT OFFICE.

OTTO MACKENSEN, OF JENA, GERMANY, ASSIGNOR TO THE FIRM F CARL ZEISS, OI"

' 'JENA, GERMANY.

SIGHTING DEVICE FOR AIRCRAFT.

Application filed August 13, 1921,

To all whom it may concern:

Be it known that I, ()T'ro MAoKENsEN, a citizen of the German Empire, residing at Jena, Germany, have invented a new and useful Sighting Device for Aircraft (for which I have filed an application in Germany, August 13, 1917; Austria, June 24, 1918; England, July 8, 1920; and Italy, July 10, 1920), of which the following is a specification.

The present invention relates to a sighting device for air-craft, having a sighting line, the inclination of which relative to the vertical in the vertical'plane containing the direction of flight is adjustable according to the aiming oif angle, which is determined by the equation e t-It In this equation '12,; is the resultant velocity tan a from the own velocity of the air-craft anc the wind velocity, i. e. the velocity of the air- 5 craft relative to the earth, H is the height of the air-craft above the earth, t the time taken from the fall of a bomb this height and R the backward drift of the bomb, i. e. that distance, by which the bomb w lags relatively to the point, in which, assuming a vacuum, it would reach the earth, under the assumption that this air resistance acts only in the plane of flight.

In the annexed drawing Fig. 1 is a diagrammatic view, whilst Fig. 2 is a view, partly in vertical section and Fig. 3 a section on the line 33 of Fig. 2.

In Fig. 1 A is the locus of an air-craft at i the height H over a point A on the earth,

velocity relative longitudinal direction (supplied and on which a wind veso that the air-craft experiences a velocity relative to the earth 01;. 5 Assuming a vacuum, abomb dropped from athe air-craft would reach the earth, assum: ing there to be no wind, at B, and allowing for a wind velocity o at C, AB being parallel to '0 and, if t be the time taken by a bomb in dropping, equal to v t, and BC being parallel to 1)... and equal to o t. Under the influence of the air resistance, however, the bomb does not reach the point C, but experiences a backward drift R. The construction of the hitherto known sighting devices of acting in its by its motor), locity 4)., acts,

" the bomb 1 only the assumption to be dropped from' to the air v Serial No. 492,111,

this kind is based on the assumption, that the air resistance is active only in the vertical plane determined by the direction of flight and that thus this backward drift R- is directed parallel to 4),; and the bomb will hit the earth inD. To this assumption there corresponds an aiming oft angle in this ver-- tical plane,-determined by the equation to be deduced from the figure However, as experience has shown, the backward drift is actually parallel to w so that will strike the ground in Z, this point being the further from D, the greater the angle {5, which is contained by the velocity 1). and the velocity 'v relative to the earth. For the case (5:0, i. e., when the aircraft is flying with the wind or against the wind, Z and D coincide. Hence, in this case was valid. For every be a correction of the other case there must inclination of the line of sight.

This correction is made possible according to the invention by a special arrangement being provided, by means of which there may be given to the line of sight on the one hand an alteration of inclination falling in the vertical plane determined by the direction of flight and on the otherhand an alteration of inclination directed perpendicularly to the said vertical plane. If in Fig. -1 the plumb be dropped onto AC, cutting this line in E, the alteration of inclination falling in this ,vertical plane. (the alteration of the aiming off) is represented by the angle DAE:e and the alteration of-inclination perpendicular to this vertical plane (the alteration of the lateral direction) by the angle EAZ::6,these angles being determined, as maybe easily deduced from the figure, by the following equations:

tan RI(I1-cos B) cos a Md-Ra 00S B)s1n'oz R sin 6 cos e Assuming a plane asbeing laid below 'A, at I ing level Within range), the said plane Will cut the rays AE, AD and AZ in E D and Z respectively, from which it follows, that Now supposing a sighting device (e. g. a diopter containing a notch and a bead), in which by means of two members (by the notch and the bead) two points of the line of sight are determined, to be so arranged that one of the members (the notch) determines the point A of the line of sight and the other member (the bead) determines that point of the line of sight lying in the said plane, this latter member, for effecting the said correction of the inclination of the line of sight, must be displaced within the assumed plane in the direction of flight by the amount a (during which it moves from D to E and in the direction of the wind component perpendicular to the direction of flight by the amount 7) (during which it moves from E to Z For this setting of the member a cross-slide system, for instance. may be used. As. assuming a certain form of bomb and an invariable own velocity w of the air-craft,

the quotient and hence (Z being invariable) the value may be taken to be constant,

the settings of both slides of the cross-slide system only vary with the angle (3, which is contained by the own velocity '0 and the velocity '0 relatively to the earth, and can be easily efl'ected by means of two scales graduated according to the function ZR(1 =cos 6) cos a COS 0:

Hence, if a constant value be again assumed, a and b are not, like a and b,only variable with the angle [5, but are also variable with the aiming off angle a viz a with the square of the cosine of a and b with the cosine of a. If in this case the member of the sighting device to be set according to the additional alteration of inclination is to be brought, as stated above, into its new position by a rotation to be effected in its plane of adjustment. for the distance r, corresponding to the distance 1', of its point of otation 21 mean approximate value must be (l-cos {5) and to the function sin {1 respectively.

As may easily be seen, the said member of the line of sight can be moved from D to Z, instead of by the two displacements (L and b by a rotation in its plane of adjustment through the angle ,3. In this case the point of rotation of the member must be disposed in such a manner at the distance from D as always to lie with l) in the direction of flight and in front of D and the direction of rotation must be opposite to the direction of rotation experienced by the direction of flight under the action of the wind relative to the longitudinal direction of the air-craft.

The plane, in which one of the members of the sighting device is adjust-ably disposed, might also lie above A at the distance Z. In this case the displacements a and b of the member would have to be oppositely directed to what they were in the case discussed aboveQor, in the case where the member is adjusted by rotation. the point of rotation of the member would have to be at the distance r behind D A further form. which is especially suitable, is theone 'in which the said plane, instead of being parallel to the earth. is always perpendicular to the sighting line set in accordance with the aiming ofl' angle 0:. Then. as may be easily deduced. if the distance of the plane from A again has the value I. the value a and 7) corresponding to the said two values a and b are determined by the equations a cos 6) cos a ZR sln B cos 0:.

assumed and a small negligible error of the adjustment be put up with. In order to keep this error as small as possible on the average. it is advisable to choose the distance r in accordance with the equation:

cos a cos 04 the said vertical plane if as a sighting device a sighting be used, in the image plane ofwhich a longitudinal mark is disposed, which is rotatable relatively to the air-craft (either by itself or along with the telescope) and adjustable in the direction of flight, the

said additional alteration of inclination in which telescope being efiected by an adjustment of the objective in a plane perpendicular to its axis, a particularly convenient constructional form, if the objective be made rotatable about an axis of rotation which is parallel to its axis and becoupled with the said longitudinal mark (or with the telescope, in the case of this longitudinal mark being so disposed as to be rotatable together with the telescope) in such aflmanner that,

on .this mark being rotated, a rotationv through the same angle fin ;the opposite direction is imparted to the objective. Thereby, the axis of rotation of the objective has to be given such a positionthat, along with the objective axis, it lies in a vertical plane which is parallel to the said longitudinal mark, when the objective occupies its middle position. The telescope has then to be-disposed on the air-craft in such a manner that contains the direction of the own velocity of the air-craft, the axis of rotation of the objective lying on that side of the objective which faces the target. What was said'with reference to the relative position of the ob'ective axis and the axis of rotation of the objective applies to a telescope of the. kind, in which-the objective is the foremost optical member. In the case of a reflecting s stem being used in front of the objective, w at was said with reference to the positions ap lies to the reflected image of the two axes ormed by this reflecting. system. The'distance of the axis of -rotation of the objective from the objective axis is, according as the optical axis of the telescope remains vertical,'on the aiming oft angle a being set (if the setting .of the aiming ofi angle is-ei'fected by the setting of the sighting mark) or experiences analteration of inclination by the angle a (if the setting of the aiming ofi' angle is eifected by inclining the entire telescope or by rotating areflecting system disposed in front of'the objective) to be chosen equal to results, telescope or equal to 13 cos a x-l-cos amin,

H 2 Z being the focal length of the objective.

In Figs.2 and 3 a-sighting telescope according to the invention is shown in elevation and plan. The telescope a is journalled in a ring I) so as to be rotatable about its the principal section of the prism a fixed to the longitudinal axis X-X, thesaid ring (as is indicated by the dotted lines) being suspended in gimbals. The optical members contained by the telescope comprise an objective a ,'a collective lens a an inverting lens a an ocular (0* and in front of the objective a reflecting system, consisting of two isosceles right angled reflecting prisms a and a, one of which, a, a, which admits the light, is contained in a bush 0, which is rotatably journalled in the telescope casing and the axis of rotationof which stands perpendicularly (1m 11 this rotatable bush, the prism a is so disposed that its principal section is parallel to that of the prism a? and its reflecting surface contains the axis of rotation of the bush 0. By means of a knob c and an angle indicating device, not shown in the drawing, the bush 0 (and with it the prism a") can be set in accordance with the aiming oil angle a (ascertained in any manner). 11 the focus of the objective a a plate a". is located, on which cross-lines are marked In:

such av manner that one of the lines is parallel to the principal section of the prisms a andaif. The objective a of the telescope is carried by a ring d, which is rotatably mounted in the caslng of the telescope in such a manner that its axis of rotation Y- T the axis of rotation X- of is parallel to the telescope, that the two axes lie in a plane parallel to the principal section of the suns a and a the axis of rotation Y--Y lying on the side of the objective facing the prism a, and finally that the distance apart of the two axes has the value Z being the focal'length of the objective, R the backward drift of a bomb to be dropped from a height H and a the greatest and a the smallest aiming ofl' angle occurring. To the ring at a 'toothedwheel sector e is screwed, the pitch circle of which is concentric with the axis of rotation Y-'Y of the ring (I and which meshes through on opening a in the telescope casing with one set of teeth f of a wheel member j, which is rotatably journalled in a bearing body 9 g telescope in such a manner that its axis of rotation is parallel to that of the rin '03, and has a second set of teeth (7 whic is coaxial with the set of teeth f ith this second set of teeth f there meshes a toothed wheel .h, which is also journalled in the bearing body g g and is in engage ment with a ring of teeth 11 fixed to the ring b,-the pitch circle of which is concentric with the axis of rotation X-X of the telescope. The toothed wheel 7 therefore travels over the stationary ring of teeth 71,

on the telescope and the parts in connection therewith (gearings and prism systems being rotated about the telescope axis X--X, and in consequence of this travelling movement the objective (1 thereby experiences a displacement about its (excentric) axis of rotation Y-Y. The earing ratio of the various gears is such that, on the telescope being rotated in the ring I), the ring 03 carrying the objective a experiences a rotation through the same angle in the opposite direction. The objective at has to be mounted in the ring 0! in such a manner that its axis, with the toothed wheel hin its middle position (that shown in the drawing) relative to the ring of teeth 2', which is also the middle position of the toothed wheel sector 0 relative to the set of teeth f, coincides with the axis of rotation (XX) of the telescope.

lVhen the sighting telescope a is to be used. the ring 6 must be mounted in gimbals on an air-craft in such a manner that the axis of rotation XX, about which the telescope is rotatable in the ring I), stands vertically, and that, with the telescope in that position relatively to the ring in which the objective axis coincides with this axis of rotation X-X, the principal section of the prisms a and a lies parallel to the longitudinal axis of the air-craft. The prism a must thereby face the forward end of the air-craft. 'When using the telescope nothing further is required, than to set the prism a by means of the actuating knob 0 in accordance with the aiming oil angle a determined by the equation o h-R H and to rotate the telescope relatively to the ring 6 in such a manner, that the images of the objects observed travel through the field of View so as to be parallel to that line on the plate a which is parallel to the principal section of the prisms a and a, so that this line falls in the direction of flight. The correction of the sighting line inclination, which must be made, on a deviation occurring of the direction of flight from the direction determined by the longitudinal axis of the air-craft, then takes place automatically, on the telescope being rotated, in consequence of the thereby effected displacement of the objective a, so that, if a bomb be dropped at the moment, in which the sighting line cuts the target, on which the bomb is to be dropped, the said target will be hit.

I claim:

In a sighting device for air-craft a sighting telescope, comprising an objective, the axis of which is vertical, a longitudinal tan a= mark disposed in the image plane of the said telescope, the objective and the mark being rotatable each relatively to the aircraft about vertical axis, and means adapted to transmit-fromthe said objective to the said mark a rotation through the same angle in the opposite direction.

()TTO IVLACKEN 

